I. Field of the Invention
This invention relates generally to a method and apparatus for separating, lifting and reforming stacks or packages of layered objects into stacks of predetermined or standardized dimensions, and more particularly to a new method and apparatus for separating, lifting and restacking packages of lumber into standardized packages.
II. Prior Art and Other Considerations
In modern sawmill and lumber treatment operations, one of the most important manufacturing stages involves the arrangement of elongated timber bodies in stacks suitable for drying or pressurized chemical treating.
Currently lumber treatment mills receive untreated lumber from many different sources. The lumber arrives at the treatment mill in a stack, called a package. No standard size exists for lumber packages resulting in package heights which vary from as few as one layer to more than sixty layers, depending on the dimension of the individual members of the package and the established practice of the particular supply mill furnishing the lumber. To chemically treat the lumber, the treatment mill quite frequently must convert the different sized packages into uniform or standardized packages, the dimensions of which conform to the parameters of the treatment mill's pressurized treatment cylinders and/or market demand.
Prior art methods to date for restacking or repackaging elongated members of a stack of lumber have consisted of either board-by-board manual restacking, which is quite obviously very labor intensive, or the use of conventional lumber stackers wherein the lumber package is broken down into individual boards and then reformed into the desired size package or where the lumber is shifted from its original package one layer at a time and then reformed or restacked into a more desirable sized package.
In a prior art device of this kind, a stacked layer in its full length is shifted perpendicularly off the remainder of the package. The layer is then positioned onto a receiving structure provided near the package, whereupon the layer is taken apart. Such a device requires a very large working area due to the type of mechanical handling necessary for such repackaging technique. In addition, the operation of breaking down the lumber package layer by layer and shifting each layer out of its original package onto a receiving structure is very time consuming.
Another prior art method is to supply individual pieces of lumber to a machine which then forms a package. A device for automatically supplying working machines with individual pieces that are withdrawn from an orderly arranged stack is known from German AS No. 2,323,227. With this device, a package layer is pushed transversely off a package by means of engaging members, and the layer is then taken apart by shifting the individual pieces in their longitudinal direction. A transverse pushing, however, is possible only if the sliding surfaces of the layers in the stack are absolutely smooth. Such a device also requires all the individual pieces of a stack layer to have exactly equal thicknesses and be absolutely even, that is, not warped, bent, or the like. If the lumber in the package is not absolutely smooth, the use of a plurality of regularly spaced elements, called stickers, is required to be provided transversely between every two stack layers. Since such ideal conditions rarely occur, in practice, a transverse shifting of a stack layer is possible only when a stack with spacer elements is used.
Such a device for separating and shifting elongated members of a stack of members is shown in U.S. Pat. No. 4,417,836 to Schiepe. This device is designed to separate and laterally shift one layer of a stack of layers for repositioning and, if necessary, for further separation of the members of the layer. Restacking or reforming the layers without lateral shifting is not possible with this device nor can the device shift or reposition more than one layer of members at a time.
Another prior art device relates to an apparatus for breaking up or subdividing stacks of superimposed or overlapping panels, particularly wooden or composition boards or sheets of plywood, for feeding into the range of a rotary saw blade in a power saw or similar tool. In operation, a lifting device carries a stack of overlapping panels and cooperates with a transfer unit to supply a desired number of overlapping panels, or discrete panels, into the range of the subdividing or severing tool.
In a machine tool of the above outlined character, it is necessary to control the extent of upward movement of the lifting device in order to ensure that a requisite number of panels will be placed into the range of the transfer unit, and it is further necessary to regulate the extent of back-and-forth movement of the transfer unit in order to reduce to a minimum the length of strokes of the transfer unit. As a rule such operations are controlled by an attendant who stands or sits adjacent to a control panel with a variety of pushbuttons, knobs, levers or analogous actuating elements for the corresponding prime movers of the machine tool. In other words, it is necessary to monitor the number of panels which have been lifted into the path of movement of the transfer unit so that the latter can thereupon perform a working stroke and transfer the selected number of panels onto the table or other suitable work support of the machine tool.
The above outlined operations must be carried out by a conscientious operator in order to avoid damage to the workpieces and/or to parts of the machine tool, or injury to attendants. Furthermore, the work is time consuming if the operator is not experienced and very familiar with the operation of the controls because he or she is likely to cause the transfer unit to perform strokes of excessive length with resultant lengthening of intervals between successive severing operations. U.S. Pat. No. 4,431,358 to Jenkner attempts to improve upon the safety features of such a machine tool and to provide for more automation of same. However, while this prior art device has some limited capability for separating stacks of panels, the device is designed for specific use with a power saw or other similar machine tool and does not attempt to address the needs or objects addressed by the present invention.
At the present time, machines which have the capability to form or restack packages of elongated members are very complicated and intricate in their operation and design and typically require the use of several human operators. These prior art machines are also limited in their ability to quickly separate and restack packages of elongated members.
Inasmuch as conventional apparatus of the above type is very expensive to construct and inasmuch as proper operation of these prior art machines require at least two or more individuals, the operating costs for such conventional installations remain undesirably high.
For the above reasons, a considerable effort has been made over a long period of time to develop a method and plant according to which only a single individual would be required to perform all of the operations in connection with separating, lifting and reforming stacks of elongated members, such as lumber, into standardized or conforming packages.